The present invention relates to internal combustion engines and, more particularly, to an internal combustion engine that is significantly more efficient than those known heretofore.
Internal combustion piston engines have been familiar and ubiquitous since the days of Otto and Diesel. These engines suffer from several widely recognized deficiencies. One is that their thermal efficiencies are far less than their theoretical efficiencies according to the second law of thermodynamics. Up to 30% of the heat released by fuel combustion is absorbed by the engine cooling systems. Another 30% is devoted to engine operation, including compressing air or an air-fuel mixture in the cylinders of these engines. From 5% to 20% of the available energy may be wasted because of incomplete combustion of hydrocarbon fuels. The net result is that these engines generally have overall efficiencies between 32% and 42%.
Another deficiency of these engines is that their exhausts tend to contain toxic substances: carbon particles and carcinogenic hydrocarbons because of incomplete combustion, and nitrogen oxides formed at the high (1800xc2x0 C. to 2000xc2x0 C.) combustion temperatures that characterize these engines. A third is that they provide power by transforming the reciprocating motion of their pistons to the rotary motion of their crankshafts. When the fuel-air mixture in a cylinder of an internal combustion engine explodes, the piston is at or near top dead center. At this position, the moment arm, across which the rod connecting the piston to the crankshaft transfers force to the crankshaft, is close to zero. Therefore, the piston exerts minimal torque on the crankshaft. As the piston moves down from top dead center, the moment arm through which the piston transfers force increases, but in the meantime the combustion gases expand somewhat, losing some of their propulsive force, so that the maximum torque exerted on the crankshaft is less than the maximum torque that could be exerted if the force of the piston could always be transferred to the crankshaft at maximum moment arm. Several attempts have been made to address some of these deficiencies.
Ferrenberg et al. (U.S. Pat. No. 4,928,658) use a heat exchanger to preheat the input fuel and air of an internal combustion engine with some of the heat of the exhaust gases. Loth et al. (U.S. Pat. No. 5,239,959) ignite the fuel-air mixture in a separate combustion chamber before introducing the burning mixture to the cylinder, in order to attain more complete combustion and inhibit the formation of nitrogen oxides.
Forster (U.S. Pat. No. 5,002,481) burns a mixture of fuel, air and steam. This mixture burns at a relatively low temperature of about 1400xc2x0 C., and nitrogen oxides are not formed. Gunnerman (U.S. Pat. No. 5,156,114 and in RE35,257) burns a mixture of hydrocarbon fuel and water, but requires a hydrogen-forming catalyst to achieve the same power with his mixture as with ordinary gasoline. Each of these prior art patents addresses only one of the defects of reciprocating internal combustion engines. None addresses the problem in its totality. U.S. Pat. No. 5,797,366, which is incorporated by reference for all purposes as if fully set forth herein, and co-pending U.S. patent application Ser. No. 09/069,545, describe an engine that further addresses the outstanding deficiencies of existing internal combustion engines. Firstly, in this engine, the axis of rotation of the power shaft of the engine is perpendicular to the plane of motion of the piston. The piston is connected to the power shaft of the engine, and the force of the piston always is applied to the power shaft at a constant moment arm perpendicular to that axis of rotation, so that maximum torque is imposed on the power shaft.
Secondly, in this engine, high pressure steam is extracted from the cooling system and returned to the combustion chambers, thus preventing severe heat loses and increasing thermal efficiency. Thirdly, ecologically it is a desirable engine in which a mixture of fuel, air and steam is burned in one or more combustion chambers, each combustion chamber being defined by a toroidal combustion chamber housing, a piston and a valve. The mixture is burned at a temperature of about 1800xc2x0 C. which is by about 200xc2x0 C. lower than the combustion temperature in existing internal combustion engines, thereby minimizing the formation of nitrogen oxides and reducing the warming up of the globe.
Yet, the toroidal engine of U.S. Pat. No. 5,797,366 and co-pending U.S. patent application Ser. No. 09/069,545 has a principle drawback; the volume of the combustion chamber increases as the burning mixture pushes the piston away from the valve. This increase in volume, before the mixture is entirely burned, tends to decrease the thermodynamic efficiency of this engine. The engine described in PCT Application US99/19315, which is incorporated by reference for all purposes as if fully set forth herein, and in U.S. application Ser. Nos. 09/146,362 and 09/250,239 is free from this drawback because the combustion stage there, takes place at a constant volume.
Thus, the thermodynamic efficiency of the combustion stage of the engine described in PCT application US99/19315 and in U.S. application Ser. Nos. 09/146,362 and 09/250,239 is superior to the efficiency of the corresponding engine which is described in U.S. Pat. No. 5,797,366 and co-pending U.S. patent application Ser. No 09/069,545, and therefore it represents a very efficient engine from the mechanical, and thermodynamical standpoints.
In order to construct and to operate this engine, its basic mechanical design has to be accompanied by a thermal design which will address the main point of its cooling and the prevention of heat loses during its operation.
Yet, even this engine has some thermal inefficiency which is related to its heat loses. It is known that rotary internal combustion engines have unique dynamic thermal control problems which are partly described in U.S. Pat. No. 3,964,445 to Ernest, et al. Summing up briefly: The inner surface of the rotor housing is subjected to higher temperatures and to much greater temperature extremes as compared to the inner surfaces of the cylinders of the reciprocating engines.
The uneven temperature distribution along the inside of the toroidal chamber and the need to dissipate large quantities of heat, dictate the use of a good heat conductor, consisting of aluminum alloy, as the housing material, even so, the Wankel engines which have a housing made of aluminum, and which are the only type of rotary engine which have achieved commercial success, can be cooled efficiently only because the large surface-to-volume ratio of their combustion and expansion chambers.
It appears that regulating and stabilizing the temperature of a rotary engine during operation and minimizing heat loses to surrounding are apparently two contradicting objects which their simultaneous fulfillment is yet an unsolved problem.
As a result most rotary internal combustion engines did not live to their expectations, and it is impossible to utilize their basic advantages.
I have discovered that: in the engine of PCT Application US99/19315, raising the temperature of the inner surface of the toroidal chamber in general, and of tile inner surface of the combustion chamber in particular, to 650xc2x0 C.-700xc2x0 C., optimizes the thermal efficiency of the engine, provided that the engine can be cooled effectively, without wasting the heat absorbed by the coolant. This leads to an improvement of the engine.
The present invention is the thermal design of a toroidal internal combustion engine, aimed to enable this temperature range of the inner walls of the combustion chamber, which includes the selection of the appropriate materials for its construction, and method of its stable operation.
According to the present invention there is provided an engine including: (a) at least one housing; (b) a rotor, rotating within the at least one housing, and (c), a mechanism for supplying fuel and air to the at least one housing, combustion of said fuel in said air then driving said rotation of the rotor; wherein, in at least one of said at least one housing, at least one component, selected from the group consisting of the rotor, and the at least one housing, is made of a material having a thermal conductivity no greater then that of iron.
According to the present invention there is provided an engine including, (a) at least one housing; (b) a rotor, rotating within said at least one housing, and (c) a mechanism for supplying fuel and air to the at least one housing, combustion of the fuel in the air then driving the rotation of the rotor; wherein the surface of at least one component selected from the group consisting of the rotor and, a portion of said housing that is in contact with combusting gases, is lined with a layer of heat resistive material.
According to the present invention there is provided an engine including, (a) at least one housing; (b) a rotor, rotating within the at least one housing, (c) a mechanism for supplying fuel and air to the at least one housing, combustion of said fuel the air then driving the rotation of the rotor, and (d) at least one cooling flow channel to carry aqueous cooling medium in the at least one component selected from the group consisting of the at least one housing, and the rotor, further comprising; a mechanism for leveling and regulating heat fluxes into the aqueous cooling medium, to ensure that the heat fluxes will be no greater then about 120 W/cm2.
According to the present invention there is provided a method for operating an engine having a combustion zone and a cooling flow channel wherein, an aqueous cooling medium is at least partially converted into steam while cooling hot gases in the combustion chamber of the engine, comprising the steps of: (a) burning a fuel-air-stream mixture in the combustion zone; (b) withdrawing at least some of the steam from the flowing cooling channel; and, (c) introducing a fuel-air mixture together with the withdrawn steam to the combustion zone.
According to the present invention there is provided a method for using gases of combusted fuel for generating mechanical power in an engine, comprising the steps of: (a) providing an engine having two housings, for each said housing, a rotor rotating within said housing, a mechanism for supplying fuel and air to at least one of said housings, combustion of said fuel in said air then driving rotation of said rotor; and, (b) delivering gases of said combusted fuel from said housing in which said combustion takes place to said other housing.
According to the present invention there is provided an engine, comprising: (a) two housings; (b) for each of the two housings: a rotor, rotatably mounted within each housing, the rotor and each housing defining between them a toroidal chamber, the rotor including at least one piston projecting into the toroidal chamber, each of the at least one piston including a leading face and a trailing face; and, (c) for each the housing, at least one valve, movably mounted within each housing; wherein a combustion region of substantially constant volume is bounded by the leading face of the at least one piston of a first of the two housings while the at least one piston approaches the at least one valve of the first housing, and by the trailing face of the at least one piston of a second of the housing while the at least one piston departs the at least one valve of the second housing.
The present invention follows the mechanical design of the engine described in PCT application US99/19315. Like the prior art engine of U.S. Pat. No. 5,797,366 and co-pending U.S. patent application Ser. No. 09/069,545, the engine of the present invention includes one or more housings with toroidal interiors. Within each housing rotates a rotor to which is attached one or more pistons that projects into the toroidal interior of the housing. The rotor and the housing define between them a toroidal chamber. One or more valves in the housing alternately seals the region between itself and an approaching or departing piston or moves to allow the piston to pass.
Like the prior art engine of U.S. Pat. No. 5,797,366 and co-pending U.S. patent application Ser. No. 09/069,545, the engine of the present invention includes provisions for engine cooling by water, superheated water steam that is produced in cooling flow channels which run throughout the engine body, and is partially injected as steam into the combustion chamber to increases the thermal efficiency of the engine and to lower the combustion temperature.
One difference between the engine of the present invention and the engine of U.S. Pat. No. 5,797,366 and co-pending U.S. patent application Ser. No. 09/069,545, is that in the preferred embodiment of the engine of U.S. Pat. No. 5,797,366 and co-pending U.S. patent application Ser. No. 09/069,545, separate toroidal chambers are used for compression, combustion and expansion, and combustion occurs there in a steadily increasing volume; whereas in the engine of the present invention, the valves, the pistons, the rotor, or some combination thereof, define a combustion region of approximately constant volume in which combustion takes place as the valve or valves move to accommodate the transit of the one or more pistons.
This allows the engine of the present invention to operate according to the more efficient Trinkler cycle: A mixture of compressed air, steam and fuel introduced into the combustion region by the cooperative motion of the pistons and the valves burns therein at approximately constant volume. The burning mixture then is released to an expansion region, where more fuel is injected to continue the burning and keep the expanding mixture at least initially at approximately constant pressure. The difference between the present invention and the invention in PCT application US99/19315, is that former applications dealt exclusively with the mechanical description of the engine, while the present invention discloses its thermal design and the materials which have to be used in order to enable its construction and subsequent steady state operation in optimal thermal conditions.
The heart of the invention is the design, construction and method of operation of an engine in which the temperature of the inner walls of the combustion and expansion chamber during steady state operation will stay uniformly distributed, constant with time at a value of 650xc2x0 C. to 700xc2x0 C. We refer to this situation as thermo-stabilization of the engine.
Thermo-stabilization is achieved by balancing apparently two contradicting effects; (a) increasing the temperature of the inner surface of the combustion and the expansion chambers, and (b); an effective heat removal from the body of the engine.
The increase of the temperature of the inner walls, which are in contact with the burning gases produced during the combustion, is aimed to diminish the rate of cooling of these gases by the walls and thus, contributes to efficiency by lowering pressure decrease inside the expansion chamber during the stroke.
The way by which this increase in the temperature of the interior walls of the chambers is achieved, is by the use of constructing materials with average lower heat conductivity than the heat conductivity of the constructing material of existing internal combustion engines, e.g. the use of iron alloys such as cast iron or steel instead of aluminum alloys.
Consequently, the engine loses less heat to surrounding, and has to be alternatively forced cooled by circulating water in cooling flow channels which are bored in the housing, in the rotor and in the valve. This forced cooling system has to be more efficient then the existing cooling system for internal combustion engines.
Here, an effective cooling method is provided, which is based on the physical effect known as xe2x80x9cboiling heat transferxe2x80x9d in which a liquid dissipates heat from its cooled object by absorbing heat because of its partial evaporation.
The liquid which is conducted in cooling flow channels bored in the body of the member to be cooled, may be driven by a pump or moves in its channels by other means, e.g. centrifugal forces. If the liquid is water moving in its channel at a speed of about 0.5-0.8 m/sec, its coefficient of boiling heat transfer is between 5 W/(cm2 degree C.) and 10 W/(cm2 degree C.), as taught in U.S. Pat. No. 5,977,714 to Adamovski.
The cooling by the mechanism of xe2x80x9cboiling heat transferxe2x80x9d requires uniform and controlled heat fluxes along the circumference of the cooling flow channel which is in contact with the water. It is necessary to limit the dissipated heat flux to about 120 W/cm2, otherwise the water in the hotter part of the channel will boil vigorously in the mechanism of xe2x80x9cfilm boilingxe2x80x9d and lose contact with the inside wall of the channel. To achieve this uniformity and control, the heat conductivity of the block of material in which the cooling channels run, is locally modified by insertions, which have heat conductivities different than that of the block material.
The water, which boils in the cooling flow channel, becomes a high-pressure hot steam (100 Kg/cm2 at 300xc2x0 C.), This steam is introduced into the compression chamber of the rotary engine together with fuel injection. Thus, the heat collected during cooling is not dissipated; instead, it produces some extra work because the injected steam expands as it is heated during the combustion.
The combustion mixture which includes air, hot steam and fuel vapor, does not degrade the power of the engine in comparison to the power produced by the steam less mixture, and it has the advantage, that the combustion temperature is lowered and hence, less poisonous nitrogen oxide is formed.
Accordingly, the scope of the invention also includes a protocol for injecting fuel, air, steam and even burned gases into the combustion chamber. The fuel is a fluid (liquid or gas) hydrocarbon or mixture of hydrocarbons, such as gasoline, diesel fuel, kerosene, an alcohol such as ethanol or methanol, propane, butane, and natural gas. If the flash point of the injected fuel is sufficiently low, it ignites spontaneously. Otherwise, the fuel is ignited by conventional ignition means such as a spark plug.
The disclosures in the present invention are applicable to internal combustion engines in general, and to rotary internal combustion engines in particular, thus it is the object of the present invention to provide an internal combustion engine with improved thermal efficiency.
It is another object of the present invention to provide an internal combustion engines with low heat loses.
It is another object of the present invention to provide an internal combustion engine, which is more economical on fuel than prior art engines.
It is another object of the present invention to provide an internal combustion engine, which is more reliable than prior art engines.
It is another object of the present invention to provide an internal combustion engine that has minimum impact on the environment.
It is another object of the present invention to provide an internal combustion engine, which contributes less nitrogen-oxide pollutants during its operation than prior art engines.
It is another object of the present invention to provide an internal combustion engine, which contributes less heat to the environment than prior art engines.
Other objects of the invention will become apparent upon reading the following description taken in conjunction with the accompanying drawings.